linux-kernel - [PATCH 19/19] perf symbols: Adjust symbol for shared objects

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Date:	Thu,  7 Apr 2016 17:58:40 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org, Wang Nan <wangnan0@...wei.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Cody P Schafer <dev@...yps.com>,
	He Kuang <hekuang@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
	Kirill Smelkov <kirr@...edi.com>,
	Li Zefan <lizefan@...wei.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	pi3orama@....com, Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 19/19] perf symbols: Adjust symbol for shared objects

From: Wang Nan <wangnan0@...wei.com>

He Kuang reported a problem that perf fails to get correct symbol on
Android platform in [1]. The problem can be reproduced on normal x86_64
platform. I will describe the reproducing steps in detail at the end of
commit message.

The reason of this problem is the missing of symbol adjustment for normal
shared objects. In most of the cases skipping adjustment is okay. However,
when '.text' section have different 'address' and 'offset' the result is wrong.
I checked all shared objects in my working platform, only wine dll objects and
debug objects (in .debug) have this problem. However, it is common on Android.
For example:

 $ readelf -S ./libsurfaceflinger.so | grep \.text
   [10] .text             PROGBITS         0000000000029030  00012030

This patch enables symbol adjustment for dynamic objects so the symbol
address got from elfutils would be adjusted correctly.

Now nearly all types of ELF files should adjust symbols. Makes
ss->adjust_symbols default to true.

Steps to reproduce the problem:

  $ cat ./Makefile
  PWD := $(shell pwd)
  LDFLAGS += "-Wl,-rpath=$(PWD)"
  CFLAGS += -g
  main: main.c libbuggy.so
  libbuggy.so: buggy.c
	gcc -g -shared -fPIC -Wl,-Ttext-segment=0x200000 $< -o $@
  clean:
	rm -rf main libbuggy.so *.o

  $ cat ./buggy.c
  int fib(int x)
  {
      return (x == 0) ? 1 : (x == 1) ? 1 : fib(x - 1) + fib(x - 2);
  }

  $ cat ./main.c
  #include <stdio.h>

  extern int fib(int x);
  int main()
  {
     int i;

     for (i = 0; i < 40; i++)
         printf("%d\n", fib(i));
     return 0;
 }

 $ make
 $ perf record ./main
 ...
 $ perf report --stdio
 # Overhead  Command  Shared Object      Symbol
 # ........  .......  .................  ...............................
 #
     14.97%  main     libbuggy.so        [.] 0x000000000000066c
      8.68%  main     libbuggy.so        [.] 0x00000000000006aa
      8.52%  main     libbuggy.so        [.] fib@plt
      7.95%  main     libbuggy.so        [.] 0x0000000000000664
      5.94%  main     libbuggy.so        [.] 0x00000000000006a9
      5.35%  main     libbuggy.so        [.] 0x0000000000000678
 ...

The correct result should be (after this patch):

  # Overhead  Command  Shared Object      Symbol
  # ........  .......  .................  ...............................
  #
      91.47%  main     libbuggy.so        [.] fib
       8.52%  main     libbuggy.so        [.] fib@plt
       0.00%  main     [kernel.kallsyms]  [k] kmem_cache_free

[1] http://lkml.kernel.org/g/1452567507-54013-1-git-send-email-hekuang@huawei.com

Signed-off-by: Wang Nan <wangnan0@...wei.com>
Acked-by: Namhyung Kim <namhyung@...nel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Adrian Hunter <adrian.hunter@...el.com>
Cc: Cody P Schafer <dev@...yps.com>
Cc: He Kuang <hekuang@...wei.com>
Cc: Jiri Olsa <jolsa@...nel.org>
Cc: Kirill Smelkov <kirr@...edi.com>
Cc: Li Zefan <lizefan@...wei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc: Zefan Li <lizefan@...wei.com>
Cc: pi3orama@....com
Link: http://lkml.kernel.org/r/1460024671-64774-3-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/util/symbol-elf.c | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/tools/perf/util/symbol-elf.c b/tools/perf/util/symbol-elf.c
index bc229a74c6a9..3f9d6798bd18 100644
--- a/tools/perf/util/symbol-elf.c
+++ b/tools/perf/util/symbol-elf.c
@@ -709,17 +709,10 @@ int symsrc__init(struct symsrc *ss, struct dso *dso, const char *name,
 	if (ss->opdshdr.sh_type != SHT_PROGBITS)
 		ss->opdsec = NULL;
 
-	if (dso->kernel == DSO_TYPE_USER) {
-		GElf_Shdr shdr;
-		ss->adjust_symbols = (ehdr.e_type == ET_EXEC ||
-				ehdr.e_type == ET_REL ||
-				dso__is_vdso(dso) ||
-				elf_section_by_name(elf, &ehdr, &shdr,
-						     ".gnu.prelink_undo",
-						     NULL) != NULL);
-	} else {
+	if (dso->kernel == DSO_TYPE_USER)
+		ss->adjust_symbols = true;
+	else
 		ss->adjust_symbols = elf__needs_adjust_symbols(ehdr);
-	}
 
 	ss->name   = strdup(name);
 	if (!ss->name) {
-- 
2.5.5